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A destroyed home on Chickering Street where authorities say Leonel Rondon, 18, of Lawrence, Mass., was killed while seated in his car in the driveway, is seen, Friday. Dozens of houses in Lawrence, Andover and North Andover caught fire from the natural gas explosions. CJ GUNTHER/EPA-EFE

Firefighters work to extinguish a fire caused by over pressurized gas lines on Sept. 13, 2018, in Lawrence, Mass. Dozens of fires broke out in Lawrence, North Andover and Andover because of the gas lines. SCOTT EISEN/GETTY IMAGES

A member of the Red Cross unloads a truck of donations to waiting volunteers outside the Parthum School in Lawrence, Mass., Friday. Multiple houses were damaged Thursday afternoon from gas explosions and fires triggered by a problem with a gas line that feeds homes in several communities north of Boston. MARY SCHWALM/AP

Children sleep as their families take shelter from the Red Cross at Arlington Middle School in Lawrence, Thursday, after a series of natural gas explosions that affected areas north of Boston. AMANDA SABGA/AP

A worker with Columbia gas stands over an open man hole as the crew works to make sure there are no gas leaks at the corner of Parker and Salem Streets in Lawrence, Mass., Friday. Multiple houses were damaged Thursday afternoon from gas explosions and fires triggered by a problem with a gas line that feeds homes. MARY SCHWALM/AP

Officials from the town of Lawrence walk past a destroyed home on Chickering Street in Lawrence, Mass. A series of reported gas explosions in towns north of Boston Massachusetts set homes ablaze and forced the mandatory evacuation of residents. CJ GUNTHER/EPA-EFE

Residents leave their neighborhood with belongings after collecting what they need for the next few days after being advised they could not stay in their homes in Lawrence, Mass. following gas line explosions. CJ GUNTHER/EPA-EFE

Firefighters battle a fire in a house in Lawrence, Mass. on Sept. 13 2018. A series of reported gas explosions in towns north of Boston Massachusetts set homes ablaze and forced the mandatory evacuation of residents. CJ GUNTHER, EPA-EFE

Firefighters search for a way into a house to check the gas line in Lawrence, Mass. on Sept. 13, 2018. A series of reported gas explosions in towns north of Boston Massachusetts set homes ablaze and forced the mandatory evacuation of residents. CJ GUNTHER, EPA-EFE

A house is destroyed in Lawrence, Mass., Thursday, Sept. 13, 2018 after a series of fires and possible gas explosions in the area. First-responders continued to fight fires in Lawrence, Andover and North Andover Mass. Carl Russo, The Eagle-Tribune, via AP

In this image take from video provided by WCVB in Boston, flames consume a home in Lawrence, Mass, a suburb of Boston, Thursday, Sept. 13, 2018. Emergency crews are responding to what they believe is a series of gas explosions that have damaged homes across three communities north of Boston. WCVB via AP

Multiple fire trucks from surrounding communities arrive Thursday, Sept. 13, 2018, in Lawrence, Mass., responding to a series of fires triggered by a problem with a gas line that feeds homes in several communities north of Boston. Phil Marcelo, AP

In this image take from video provided by WCVB in Boston, firefighters battle a large structure fire in Lawrence, Mass, a suburb of Boston, Thursday, Sept. 13, 2018. Emergency crews are responding to what they believe is a series of gas explosions that have damaged homes across three communities north of Boston. WCVB via AP

Firefighters battle a house fire, Thursday, Sept. 13, 2018, on Herrick Road in North Andover, Mass., one of multiple emergency crews responding to a series of possible gas explosions and fires triggered by a problem with a gas line that feeds homes in several communities north of Boston. Mary Schwalm, AP

In this image take from video provided by WCVB in Boston, flames consume the roof of a home in Lawrence, Mass, a suburb of Boston, Thursday, Sept. 13, 2018. Emergency crews are responding to what they believe is a series of gas explosions that have damaged homes across three communities north of Boston. WCVB via AP

“We need to turn over every stone and shine a light on the workings of this company and the entire industry, so that people can both trust that their gas system is safe and verify that nothing like this will ever happen again," Markey said. "The fate of families and small businesses depends on it.”

Distribution pipelines operated by local natural gas utilities often operate at different pressures throughout the systems. The Columbia Gas system in Lawrence used 14 different gas regulators to ramp the pressure up or downas gas moves to customers.

Low pressure can be dangerous. When sensors detect a loss of pressure, systems compensate by adding more gas.

A Columbia Gas control room in Ohio noticed the pressure spike at 4:04 p.m. The first 911 call for a house fire came at 4:11 p.m.

The NTSB investigators say the work crews followed the instructions they were given.

"Columbia Gas developed and approved the work package executed on the day of the accident," the NTSB investigators say in their preliminary report. "The work package did not account for the location of the sensing lines or require their relocation to ensure the regulators were sensing actual system pressure. The work was performed in accordance with steps laid out in the work package."

The NTSB said it will continue to investigate Columbia Gas procedures and its coordination with emergency responders once it noticed the pressure spike.

Nisource, the parent company of Columbia Gas, said it was cooperating with the investigation, but would not discuss it until the final report is issued.

"However, we can say that, because safety is our top priority, in the hours immediately after the incident we suspended similar work and enhanced procedures related to our low pressure systems," Nisource President Joe Hamrock said in a statement. "We saw these as responsible steps to take in the aftermath of the incident and while the facts were being gathered."

In this image take from video provided by WCVB in Boston, flames consume a home in Lawrence, Mass, a suburb of Boston, on Sept. 13.(Photo: WCVB via AP)